The invention relates to fuel injection system incorporating means for distributing the fuel charge to each cylinder over the engine cycle during start-up to improve the engine starting characteristics. Examples of a fuel injection system in which the present invention may be used are disclosed in my U.S. patent application, Ser. No. 629,421, entitled "Fuel Injection System" and in my U.S. patent application Ser. No. 629,443, entitled, "A Control Computer for a Fuel Injection System" both filed concurrently herewith on Nov. 6, 1975.
In the past few years interest in fuel injection systems has been spurred because of the decrease in pollutants contained in the auto exhaust emissions of fuel injection equipped cars as compared to cars equipped with conventional carburetors. This improvement results from the greater precision of fuel metering to each cylinder achieved by fuel injection systems.
Recent fuel injection systems have typically fired the injections, singly, in sequence over the engine cycle, or arranged the injector in groups of two or three according to firing order and staggered the firing of the groups over the cycle. The injection time provided by these prior art arrangements may differ appreciably from those injection times which would make it easiest to start the automotive engine. During cold start-up, there is no emission advantage to injecting fuel with reference to a particular crankshaft angle. Further, the quantity of fuel injected during cold start-up is extremely critical if flooding, an overly rich or lean starting mixture with its attendant high levels of exhaust pollutants is to be avoided. The quantity of fuel to be injected to achieve quick start-up will vary principally with ambient temperature, and the condition of the fuel, that is, the specific volatility of the fuel in the tank.
The quantity of fuel injected into a cylinder during starting, based on the measurement of the normal engine operating parameters, may not be a proper amount to create the fuel air mixture in the cylinder for flammability. The exact amount of fuel required to achieve this condition varies in a complicated manner as a function of a number of parameters including the exact air to fuel required ratio in combination with the volatility of the particular volume of fuel being injected. For these reasons considerable difficulty may be encountered in starting the vehicle with a conventional fuel system.
I have found that pollutant level in emissions may be controlled to a noticeable degree by control of the time of the injection pulse relative to the engine cycle. An injected fuel charge may be heated by contact with the intake valve area to partially vaporize the charge and increase the speed of vaporization of the remainder of the charge when it is drawn into the hot cylinder. By injecting the fuel into the intake valve area as soon as possible after the valve closes, this heating action is maximized.